1. Field of the Invention
The present invention relates to a substrate, such as a glass substrate, used for a liquid crystal display device and having a repaired defect in a metallic pattern or a mask of a semiconductor formed on the substrate and, and a method and a device for repairing the metallic pattern or the mask of the semiconductor on the substrate.
2. Description of Related Art
In recent years, a matrix type display device using a liquid crystal has been used widely as a display device for a computer instead of a display device using a cathode ray tube. Further, to increase the data displayed on a screen at one time, a liquid crystal display device or a plasma display device having a large screen or high definition has been developed. This has reduced yield and has increased defective substrates, and hence, the defective substrates are repaired to reduce costs of liquid crystal display device.
An ordinary matrix type liquid crystal substrate is formed by etching transparent X and Y electrodes comprising ITO on two glass substrates. Then, the substrates are arranged opposite to each other, such that the electrodes form a planar matrix pattern. The glass substrates are then filled with liquid crystal. When the X electrodes or the Y electrodes are formed on the substrates as described, the defects shown in FIG. 9 are sometimes produced by mixed foreign matter or by etching defects. FIG. 9A shows a good product and FIG. 9B shows a short-circuited defect in which neighboring lines are joined to each other and FIG. 9C shows a broken (open) defect in which a line is broken.
To repair the short-circuit defect shown in FIG. 9B, a short repair device, that is, a device for cutting a short-circuited part by laser irradiation has been-used.
To repair the open defect shown in FIG. 9C, the following methods have been disclosed;
(W) an organoindium compound solution is applied to the open defect and then is heated to transform the applied film of the organoindium compound into a conductive layer (Japanese Unexamined Patent Application No. 3-85523),
(X) a conductive liquid glass is applied to a defective part of a transparent electrode (Japanese Patent Application Laid-Open No. 2-67517),
(Y) an adhesive comprising fine plastic particles is applied to an open defect of a bump (Japanese Patent Application Laid-open No. 2-301723),
(Z) a conductive material is applied to an open defect and then laser irradiation is applied thereto (Japanese Patent Application Laid-Open No. 2-301723).
However, the above-mentioned techniques disclosed in (W) to (Z) have several drawbacks. For example, in the method disclosed in (W), the indium metal is oxidized when it is heated to form a conductive layer. Also, the oxidation is detrimental to the electric characteristics and the oxidation process produce a large amount of heat.
In the method disclosed in (X), the conductive glass used for repairing the open defect in the electrode produces large resistance, and the process generates a large amount of heat when repairing the defect. Similarly, the method disclosed in (Y) has structural problems in that resin containing conductive fine particles produces a large resistance and a large amount heat is needed in the process used to form the joined part. Further, a thick coated film needs to be used so as to realize a stable joining state.
In the method disclosed in (Z), a device referred to as a YAG laser for heating the conductive material is large in size and troublesome to handle. Also, because the output of the device cannot be freely controlled, the conductive material is rapidly baked and cooled, which can produce cracks in the repaired part. A carbon dioxide laser instead of the YAG laser has been used for baking, but any laser has advantage and disadvantage form the viewpoint of the useable life of the laser and handling of laser.
Further, since a line of a transparent electrode formed on the substrate of the liquid crystal display device is very small in width and in thickness, when the above-mentioned organ indium compound, the conductive glass or the adhesive containing conductive fine particles are used, it is difficult to make the joined part very thin. Even if the joined part can be made thin, the quality of the joined part is not ensured because cracks are produced in the joined part.
Furthermore, when the transparent electrode is formed on the substrate of the liquid crystal display device, a resist material is applied to a thin film and is exposed to light by using a mask and is developed to form a resist pattern. Then the above-mentioned thin film is etched according to the resist pattern to form a transparent electrode having a predetermined pattern. In this regard, if the above-mentioned mask has a defect, the pattern formed on the transparent electrode also has a defect. Also, opaque film of the above-mentioned mask sometimes has a defect and when the defect is repaired, the above-mentioned problems are also produced.
Still further, if the lithographic mask has a defect, the pattern is so fine that it is hard to repair the defect and hence the mask is scrapped. However, in recent years, it has been required that the defective pattern of the mask be repaired to reduce costs.